I. Field of the Invention
The present invention relates to a glass composition used for a semiconductor coating.
II. Description of the Prior Art
In general, a glass passivation layer is formed to cover and protect a p-n junction surface of a semiconductor element, such as a diode, a thyristor, and a transistor, which comprise monocrystalline silicon, so as to improve reliability and withstanding voltage. The following characteristics are required for a glass used as a glass passivation material:
(1) A high withstanding voltage should be imparted to a semiconductor by a glass coating. Furthermore, a leakage current should be decreased to less than a set limit when a reverse bias voltage is applied.
(2) Even if a blocking treatment (BT) is performed in which the element covered with a glass layer is reverse-biased and heat-treated, electrical characteristics of the element should not be degraded.
(3) When a glass coating is formed on the element, the element should become water-proof and have excellent resistance to acids. The semiconductor substrate should be stable during the photoetching process.
(4) The thermal expansion coefficient of a glass layer should be similar to that of silicon, thus substantially preventing glass cracking and wafer warpage.
Zinc borate (ZnO, B.sub.2 O.sub.3 -based) or lead silicate (PbO, SiO.sub.2 -based) glass has been conventionally used as a semiconductor coating glass. However, these materials do not sufficiently satisfy the above characteristics for the glass coating. In particular, zinc borate glass has poor resistance to chemicals, whereas lead silicate glass has poor electrical characteristics (especially BT characteristics).